On Fri, Apr 08, 2005 at 04:47:43PM -0700, Maksim Yevmenkin wrote: > Bernd Walter wrote: > >On Fri, Apr 08, 2005 at 06:12:33PM -0400, David Gilbert wrote: > > > >>Bernd> Has this device multiple interfaces? e.g. one HID and > >>another Bernd> as described. I often thought about getting ugen > >>working at Bernd> interface level too. > >> > >>Here's the output of udesc_dump on it. Right now, using the > >>current version of libusb (not the version from ports), I can use > >>usb_interrupt_write(dev, 1, "MK255", 5, 0) to send data to it --- > >>and the data is sent --- at least lights on the USB hub flash. If > >>I replace '1' with anything else, it doesn't accept it. However, > >>it doesn't seem to have opened the relays. > > > >Yes - you must use 1 - there is only one out-endpoint. 0x81 is for > >receiving data and endpoint 0 is the mandandory control endpoint. > >Interrupt Endpoints are not variable in size. Both interrupt > >endpoints are 8 Bytes, so you must read and write exact 8 Bytes per > >transfer - 5 shouldn't work for USB compliant devices. > > hmmm... i was always confused about bMaxPacketSize. i was thinking that > it limits the size of one usb transaction, and it could take several usb > transactions to transfer one data packet.
It is a bit more complicated. For control endpoints packets transfers that are bigger than one packet can be transfered using multiple packets using a shortened last packet, which can be even of 0 length if the transfer exactly fits in packets. For bulk endpoints things can be handled specific to the protocol requirements - e.g. most serials don't track transfer borders. We have interrupt endpoints - you are right smaller than max packets are allowed - just checked the specs. The remaining is the same as for bulk endpoints, but interrupt endpoint are different in bus time calculations. > for example i have a bluetooth usb dongle that has > > Standard Endpoint Descriptor: > bLength 7 > bDescriptorType 05 > bEndpointAddress 81 (in) > bmAttributes 03 (Interruput) > wMaxPacketSize 16 > bInterval 1 > > and i certanly can receive data packets from this endpoint that are more > (and less) then 16 bytes in size. so, i would guess (and i might be > wrong) that it is ok to send/receive data packets that are not equal to > bMaxPacketSize in size. As corrected above - you are really allowed to have smaller packets. But you can't have larger ones - however you can transfer multiple packets in one transaction, but this is not optimal speedwise as interrupt endpoints are laid out in a specific timeline. bInterval=1 means one packet per 1ms will be transfered and not more. Doing a transfer with e.g. 2 packets will take 1ms longer - even if the bus is idle in the meantime. This is because interrupt endpoints get garantied bus time. -- B.Walter BWCT http://www.bwct.de [EMAIL PROTECTED] [EMAIL PROTECTED] _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
